Indeed - and an electric chair will kill even if it is both properly grounded and plugged into a GFCI socket capable of handling the current (aside: do electric chairs have UL certification? I doubt it, but the states in which it is still nominally an option presumably want the operators to be safe.)

If you are put / put yourself into the normal current path (such as while working on the innards of plugged-in and switched-on equipment), you are just the load (or part of it), and neither GFCI nor previous protection schemes will help you.